<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Web 设计</title>
        <link rel="shortcut icon" href="/mylogo/logo_k_icon_72.ico" type="image/x-icon" />
    </head>
    <body>
<h1>我的第一段 JavaScript</h1>

<p>请输入数字。如果输入值不是数字，浏览器会弹出提示框。</p>

<input id="demo" type="text">

<script>
function myFunction()
{
var x=document.getElementById("demo").value;
if(x==""||isNaN(x))
    {
    alert("Not Numeric");
    }
else
{
    alert("Is Numeric !");
}
}
</script>

<button type="button" onclick="myFunction()">点击这里</button>

    </body>
</html> 

